1. Field of the Invention
This invention is related to wellbore milling processes; milling tools and whipstocks and anchors for them; and in one aspect to single-trip milling methods and systems.
2. Description of Related Art
Milling tools are used to cut out windows or pockets from a tubular, e.g. for directional drilling and sidetracking; and to remove materials downhole in a well bore, such as pipe, casing, casing liners, tubing, or jammed tools. Various prior art tools have cutting blades or surfaces and are lowered into the well or casing and then rotated in a cutting operation. With certain tools, a suitable drilling fluid is pumped down a central bore of a tool for discharge beneath the cutting blades to assist in the removal from the well of cuttings or chips.
Milling tools have been used for removing a section of existing casing from a well bore to permit a sidetracking operation in directional drilling, to provide a perforated production zone at a desired level, to provide cement bonding between a small diameter casing and the adjacent formation, or to remove a loose joint of surface pipe. Also, milling tools are used for milling or reaming collapsed casing, for removing burrs or other imperfections from windows in the casing system, for placing whipstocks in directional drilling, or for aiding in correcting dented areas of casing or the like. Prior art sidetracking methods use cutting tools of the type having cutting blades and use a deflector such as a whipstock to cause the tool to be moved laterally while it is being moved downwardly in the well during rotation of the tool, to cut an elongated opening pocket or window in the well casing.
Certain prior art operations which employ a whipstock also employ a variety of tools used in a certain sequence. That requires a plurality of "trips" into the wellbore. For example, a false base (e.g. a plug, bridge plug, packer or anchor packer) is set in a casing or in a borehole that serves as a base on which a whipstock can be set. Certain prior art whipstocks have a movable plunger which acts against such a false base. In certain multi-trip operations, a packer is oriented and set in a wellbore at a desired location. This packer acts as an anchor on or against which tools above it may be urged to activate different tool functions. The packer typically has a key or other orientation indicating member. The packer's orientation is checked by running a tool such as a gyroscope indicator into the wellbore. In this case a whipstock-mill combination tool is then run into the wellbore by first properly orienting a stinger at the bottom of the tool with respect to a concave face of the tool's whipstock or by using an MWD tool. Splined connections between a stinger and the tool body facilitate correct stinger orientation. A starting mill is secured at the top of the whipstock, e.g. with a setting stud and nut. The tool is then lowered into the wellbore so that the packer engages the stinger and the tool is oriented. Slips extend from the anchor and engage the side of the wellbore to prevent movement of the tool in the wellbore. Pulling or pushing on the tool then shears the setting stud, freeing the starting mill from the tool. Rotation of the string with the starting mill rotates the mill. The starting mill has a tapered portion which is slowly lowered to contact a pilot lug on the concave face of the whipstock. This forces the starting mill into the casing to mill off the pilot lug and cut an initial window in the casing. The starting mill is then removed from the wellbore. A window mill, e.g. on a flexible joint of drill pipe, is lowered into the wellbore and rotated to mill down from the initial window formed by the starting mill. Typically then a window mill with a watermelon mill mills all the way down the concave face of the whipstock forming a desired cut-out window in the casing. This may take multiple trips. Then, the used window mill is removed and a new window mill and string mill and a watermelon mill are run into the wellbore with a drill collar (for rigidity) on top of the watermelon mill to lengthen and straighten out the window and smooth out the window-casing-open-hole transition area. The tool is then removed from the wellbore. The prior art also discloses a variety of single-trip milling systems each of which requires that a packer, bridge plug, anchor packer, or other securement be provided as a base in a tubular upon which to position the milling.
The prior art also discloses a variety of single trip setting systems for whipstocks, usually hydraulically actuated, each of which allows circulation usually only once at setting depth, after which time pins are usually sheared and any additional pumping will only pressurize the system to actuate hydraulic setting devices.
There has long been a need for an efficient and effective single trip whipstock setting method that allows for selective pressurization or circulation while fluid is being pumped through the drillstring, and also selectively provides or prevents communication between the inside and outside of the drillstring while no fluid is being pumped through the drillstring. There has long been a need for systems effecting such a method, as well as tools useful in such a method.
There has long been a need for an efficient and effective single-trip milling method and systems for effecting the method. There has long been a need for tools useful in such a method. There has long been a need for such systems which do not require a base upon which the system is emplaced and/or which have a selectively settable anchor apparatus which does not require the dropping of a ball, dart, etc. . . .